Wereszczynski, MichalChwilka, PaulinaSmolka, EwaIlczuk, EwaOner, SezinBarzykowski, Krystian2025-08-152025-08-1520252352-3409https://doi.org/10.1016/j.dib.2025.111923Barzykowski, Krystian/0000-0003-4016-3966The present dataset comprises the performance of adult participants on two experimental tasks designed to measure working memory capacity: the Symmetry Span (SymSPAN) and Operation Span (OSPAN) tasks. Initially, a large sample of 566 participants completed these tasks online. From this pool, a random subset of individuals representing low, medium, and high levels of working memory capacity were invited to participate in two laboratory sessions. In these sessions, spaced one week apart, participants completed the same tasks again. The dataset includes complete performance data from both tasks, along with demographic information such as participants' age and gender. This relatively large dataset offers valuable opportunities for exploratory research on working memory capacity, including analyses of its relative stability, variations over time and across testing environments, individual differences, and contributions to meta-analyses. (c) 2025 The Author(s). Published by Elsevier Inc. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/)eninfo:eu-repo/semantics/openAccessWorking Memory CapacityOperation SPAN TaskSymmetry SPAN TaskOnline ExperimentArticle10.1016/j.dib.2025.1119232-s2.0-105012192435